The present invention generally relates to signal recording systems for recording information signals and a control program signal on a rotary recording medium, and more particularly to a signal recording system which obtains a time division multiplexed signal by time-division-multiplexing to the control program signal which is transmitted in terms of blocks a block discrimination signal for discriminating the beginning or end of the block and records the time division multiplexed signal on the rotary recording medium.
Heretofore, attempts have been made to more effectively utilize information signals which are recorded on a rotary recording medium (hereinafter simply referred to as a disc). Such attempts include coupling to a disc reproducing apparatus an external device such as a microcomputer which has a discriminating function, for example, and controlling the disc reproducing apparatus by the microcomputer. The control of the disc reproducing apparatus by the external device is carried out based on control programs which are recorded on the disc together with the information signals such as video and audio signals. As a result, it is possible to play the disc on the disc reproducing apparatus in the so-called interactive mode between the external device.
A signal recording system for recording the control programs described above and a disc which is recorded with the control programs, are disclosed in a U.S. patent application Ser. No. 574,521 filed Jan. 27, 1984 in which the assignee is the same as the assignee of the present application. According to this previously proposed signal recording system, a modulated signal is obtained by modulating digital data related to the control programs according to a self clock modulation system based on a reference clock having a period which is twice the horizontal scanning period of the video signal, for example. The modulated signal is then band-limited to the audio signal band, and is recorded independently on the disc or is multiplexed in time sequence with the audio signal and recorded on the disc. The control programs are written in at least down load type statements and direct statements. In the present specification, a statement which is executed after being once loaded into the external device is referred to as a down load type statement, and a statement which is executed immediately without being loaded into the external device is referred to as a direct statement.
According to the previously proposed signal recording system described before, the following superior effects can be obtained.
(a) Because the control programs are time-sequentially recorded on the disc so as to maintain a perfect one-to-one relationship with the corresponding video and audio signals, it is unnecessary to store reproduced control programs which are written in direct statements. In addition, control programs which are written in down load type statements are loaded into the external device every time the control program is reproduced, and it is possible to perform operations such as replacement, partial deletion, and addition with respect to the already stored programs. Accordingly, the memory capacity required in the external device can be kept down to a minimum.
(b) It is possible to record the control programs in the limited audio signal band, since a modulated signal which is obtained by modulating the control programs according to a self clock modulation system such as the biphase space modulation and the biphase mark modulation is recorded on the disc as a control program signal.
(c) Because the control program signal is recorded on the same tracks on the disc as the video and audio signals, the limited recording capacity of the disc is effectively utilized compared to a case where tracks are provided exclusively for recording the control program signal. With respect to the video signal, it is possible to obtain a large recording capacity which is the same as the recording capacity obtainable in the disc which is not recorded with the control program signal.
(d) When cutting the disc, it is possible to reproduce the control program signal from a master tape or a master disc as in the case of the video and audio signals and continuously record the control program signal simultaneously as the video and audio signals.
(e) By preparing a number of interpreters which are used for interpreting the language with which the programs are recorded on the disc in accordance with the total number of kinds of languages which are anticipated on being used in various external devices, the control programs which are recorded on the same kind of disc can always be written in a predetermined kind of language. Thus, compared to the conventional case where it is essential to prepare a specific number of control programs corresponding to all kinds of external devices which are anticipated on being used, even with respect to the same kind of disc, the burden on the developer of the software is greatly reduced.
(f) Because the control programs written in the down load type statements can be recorded on the disc in a scattered manner at time positions which are unrelated to the actual time positions where the control programs are executed, it is possible to increase the freedom of the recording timing with which the audio signal is recorded in a state multiplexed in time sequence with the control program signal.
However, according to the previously proposed signal recording system, the control program signal is recorded in the transmission path of the audio signal. On the other hand, the existence of the control program signal, that is, whether the control program signal is recorded, is discriminated by use of a part of an address signal which is originally used for discriminating the number of tracks, which address signal is recorded in the transmission path of the video signal. For this reason, there is a problem in that the circuit construction of a circuit which discriminates the existence of the control program signal by use of a part of the address signal becomes complex. In addition, there is a problem in that complex programs are required to control an interface which couples the disc reproducing apparatus and the external device.
Further, the processing speed of the external device and the response speed of the disc reproducing apparatus differ depending on the contents of the control commands and the timing with which the control commands are reproduced. Accordingly, in order to carry out a control in correspondence with each field of the video signal, it is necessary to discriminate the field of the reproduced video signal in one track turn when the video signal is recorded on the disc at a rate of a plurality of fields per track turn. For example, in a case where the video signal is recorded on the disc at the rate of four fields per track turn, it is necessary to discriminate which one of the four fields the reproduced video signal is related to. It is possible to reproduce a reference signal which is recorded in a vertical blanking period part of the disc, for example, and discriminate the field of the video signal based on the reproduced reference signal. The supply of the control program signal from the disc reproducing apparatus to the interface is carried out based on the above discriminated result. Hence, according to the previously proposed signal recording system, there is a problem in that the circuit construction of a discriminating circuit for discriminating at the time of the reproduction the field to which the reproduced video signal is related, becomes complex. This is because the reference signal is not always reproduced during one revolution of the disc. For example, the reference signal is not reproduced during one revolution of the disc in a case where one track turn is not scanned in its entirety but the scan is shifted from the one track turn to another track turn.